Ionic liquid treatment of vacuum slop cut to increase hydrocracking feed

ABSTRACT

A process and apparatus for increasing vacuum gas oil recovery from a vacuum column are described. The process includes separating a residue crude oil stream from a crude oil separation column in a vacuum column into at least one vacuum gas oil fraction, and a contaminant-rich slop fraction containing at least one contaminant; contacting the contaminant-rich slop fraction with a lean ionic liquid in a contaminant removal zone to produce a mixture comprising a contaminant-lean slop fraction and a rich ionic liquid comprising at least a portion of the at least one contaminant; and separating the mixture to produce a treated slop effluent comprising the contaminant-lean slop fraction and a rich ionic liquid effluent comprising the rich ionic liquid.

BACKGROUND OF THE INVENTION

Vacuum towers are important units in a refinery because they produce the feed for the secondary conversion units, such as hydrocracking and hydrotreating units, and fluid catalytic cracking (FCC) units. The operation and yields of from the vacuum towers affect the operation of the downstream conversion units. Improved vacuum tower operation is critical to meet the demands of the increasingly heavier world crude slate.

Vacuum gas oil (VGO) is a hydrocarbon fraction that may be converted into higher value hydrocarbon fractions such as diesel fuel, jet fuel, naphtha, gasoline, and other lower boiling fractions in the downstream conversion units. However, VGO feed streams have higher amounts of nitrogen and are more difficult to convert. For example, the degree of conversion, product yields, catalyst deactivation, and/or ability to meet product quality specifications may be adversely affected by the nitrogen content of the feed stream. It is known to reduce the nitrogen content of the VGO stream by catalytic hydrogenation reactions such as in a hydrotreating process unit. It is also known to remove nitrogen from the VGO stream using ionic liquids.

Increasing the VGO recovery in the vacuum tower would not only provide a large economic incentive per barrel of crude, but also reduce the need for capital expenditures. Reduced vacuum residue production resulting from deep cut tower operation helps to mitigate the effects of heavier crude slates, reducing the need for additional delayed coking capacity.

However, increasing the VGO yield while processing heavier crudes requires revamping existing columns for deep cut operations. Typical vacuum distillation units have a VGO endpoint in the range of 560° C. Deep cut vacuum operations recover more VGO by increasing the endpoint to as high as 600° C. However, the challenge is to design the column internals to minimize the amount of contaminants that come out with the VGO. The downstream hydroprocessing units are very sensitive to the contaminants in the feed VGO stream. Furthermore, there are significant equipment and utility costs associated with this type of change. For example, the feed furnace, vacuum tower, heat exchangers, and vacuum jet equipment all play important roles in the ultimate capacity, low pressure capability, and revamp cost of each specific unit. All of these factors, as well as others, must be evaluated in order to reach any conclusions concerning possible changes to the refinery.

Therefore, there is a need for improving the VGO yields without the need to change the operation of the vacuum tower significantly.

SUMMARY OF THE INVENTION

One aspect of the invention is a process for increasing vacuum gas oil recovery from a vacuum column. In one embodiment, the process includes separating a residue crude oil stream from a crude oil separation column in a vacuum column into at least one vacuum gas oil fraction, and a contaminant-rich slop fraction containing at least one contaminant; contacting the contaminant-rich slop fraction with a lean ionic liquid in a contaminant removal zone to produce a mixture comprising a contaminant-lean slop fraction and a rich ionic liquid comprising at least a portion of the at least one contaminant; and separating the mixture to produce a treated slop effluent comprising the contaminant-lean slop fraction and a rich ionic liquid effluent comprising the rich ionic liquid.

Another aspect of the invention involves an apparatus for increasing vacuum gas oil recovery. In one embodiment the apparatus includes a crude oil separation column having an inlet and at least a bottom outlet; a vacuum column having an inlet and having at least an upper and a lower outlet, the inlet of the vacuum column being in fluid communication with the bottom outlet of the crude oil separation column; a contaminant removal zone having an inlet and an outlet, the inlet of the contaminant removal zone being in fluid communication with the lower outlet of the vacuum column; a secondary conversion zone having an inlet and an outlet, the inlet of the secondary conversion zone being in fluid communication with the upper outlet of the vacuum column and the outlet of the contaminant removal zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of one embodiment of the invention.

FIGS. 2A and 2B are a simplified flow scheme showing different embodiments of the contaminant removal zone.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for increasing the VGO yields without the need to alter the existing vacuum tower significantly. In general, the invention involves removing contaminants from the slop fraction from a vacuum tower using an ionic liquid.

A slop fraction is withdrawn from the vacuum tower below the heavy vacuum gas oil (HVGO) draw. Much of the contamination will be in the slop fraction, rather than in the light VGO (LVGO) and HVGO fractions. The slop fraction is treated with an ionic liquid to remove the contaminants. The treated slop fraction can then be combined with the LVGO and HVGO fractions. Thus, the process increases the feed to the downstream processing unit without having much of an impact on the vacuum column. In addition, the vacuum residue stream is reduced due to the use of the treated slop cut.

The ionic liquid can be regenerated using known regeneration methods and recycled to the contaminant removal zone.

An extract stream rich in contaminants from the regeneration zone can be combined with the vacuum residue stream from the vacuum tower, and the combined stream can be sent to a delayed coker unit for further processing.

FIG. 1 illustrates one embodiment of the process. A crude oil stream 105 is introduced into a crude distillation zone 110 where it is separated into two or more fractions. For example, as illustrated, the crude oil stream 105 is separated into fraction 115 which contains light naphtha, liquefied petroleum gas (LPG), and offgas, which is C²⁻ hydrocarbons, heavy naphtha fraction 120, kerosene fraction 125, diesel fraction 130, heavy gas oil (HGO) fraction 135, and residue crude oil fraction 140.

The residue crude oil fraction 140 is sent to vacuum tower 145 where it is separated into two or more streams. The residue crude oil fraction can vary from 325° C.+ to 370° C.+ material depending on the unit configurations and limitations. For example, the residue crude fraction 140 can be separated into vacuum diesel fraction 150, LVGO fraction 155, HVGO fraction 160, slop fraction 165, and vacuum residue fraction 170.

In general, the LVGO fraction 155 comprises petroleum hydrocarbon components boiling in the range of from about 340° C. to 430° C., and the HVGO fraction 160 boils from about 430° C. to 550° C., or 430° C. to 520° C. The endpoint between the LVGO and the HVGO can vary from 410° C. to 450° C. depending on the characteristics of the crude and the mode of operation. The slop fraction 165 comprises components boiling in the range of about 520° C. to about 570° C. The TBP T5 point for the slop fraction is about 490° C. about to 530° C., and the TBP T95 point is about 550° C. to about 600° C. For deep cut distillation, the slop fraction can range from 520° C. to 600° C. There can be an overlap between the HVGO fraction and the slop fraction. The vacuum residue fraction 170 boils in the range of 550° C. to 600° C.

As a result of the withdrawal of the slop fraction, there is no need to pull additional VGO up the flash zone. The end point of the VGO can be kept low, and a majority of the contaminants, such as sulfur, nitrogen, metals, and Conradson Carbon Residue (CCR) will concentrate in the slop fraction. Normally, the sulfur, nitrogen, metals, and CCR content would increase with the endpoint of the VGO; thus, limiting the endpoint would improve the control of the VGO quality.

The flow of the slop fraction 165 is in the range of about 5 wt % to about 30 wt % of the total VGO stream, but the majority of the contaminants are concentrated in the slop fraction 165.

The slop fraction 165 is then contacted with ionic liquid in contaminant removal zone 175 to remove the contaminants. The term “contaminant” means one or more species found in the slop fraction 165 that is detrimental to further processing. Contaminants include, but are not limited to, nitrogen, sulfur, metals (e.g., nickel, iron, and vanadium), heavy polynuclear aromatic (HPNA) hydrocarbons, and Conradson carbon residue or carbon residue. Generally, the slop fraction 165 may contain from about 100 ppm-wt to about 30,000 ppm-wt nitrogen; from about 1000 ppm-wt to about 50,000 ppm-wt sulfur; and from about 100 ppb-wt to about 2000 ppm-wt of metals. In an embodiment, the nitrogen content of the slop fraction 165 ranges from about 200 ppm-wt to about 5000 ppm-wt. In another embodiment, the sulfur content of the slop fraction 165 ranges from about 1000 ppm-wt to about 30,000 ppm-wt.

The ionic liquid can remove one or more of the contaminants in the slop fraction 165. The slop fraction 165 will usually comprise a plurality of nitrogen compounds of different types in various amounts. Thus, at least a portion of at least one type of nitrogen compound may be removed from the slop fraction 165. The same or different amounts of each type of nitrogen compound can be removed, and some types of nitrogen compounds may not be removed. In an embodiment, the nitrogen content of the slop fraction 165 is reduced by at least about 3 wt % with respect to the feed, or at least about 5 wt %, or at least about 10 wt %, or at least about 15 wt %, at least about 20 wt %, or at least about 30 wt %, or at least about 40 wt %. The maximum removal is typically about 85 wt %.

The slop fraction 165 will typically also comprise a plurality of sulfur compounds of different types in various amounts. Thus, at least a portion of at least one type of sulfur compound may be removed from the slop fraction 165. The same or different amounts of each type of sulfur compound may be removed, and some types of sulfur compounds may not be removed. In an embodiment, the sulfur content of the slop fraction 165 is reduced by at least about 1 wt % with respect to the feed, or at least about 2 wt %, or at least 3 wt %, or at least 5 wt %, or at least 10 wt %. The maximum removal is typically about 65 wt %.

The slop fraction 165 will usually contain various metals, including, but not limited to, nickel, iron, and vanadium. In an embodiment, the metal content of the slop fraction 165 can be reduced by at least about 10% with respect to the feed on an elemental basis, or at least about 20 wt %, or at least about 25 wt %, or at least about 30 wt %, or at least about 40 wt %, or at least about 50%. The maximum removal is typically about 82 wt % for vanadium, and about 86 wt % for nickel. The metal removed may be part of a hydrocarbon molecule or complexed with a hydrocarbon molecule.

The nitrogen content may be determined using ASTM method D4629-02, Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection. The sulfur content may be determined using ASTM method D5453-00, Ultraviolet Fluorescence. The metals content may be determined by UOP389-09, Trace Metals in Oils by Wet Ashing and ICP-OES. The Conradson carbon residue may be determined by ASTM D4530. Unless otherwise noted, the analytical methods used herein such as ASTM D5453-00 and UOP389-09 are available from ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pa., USA.

Processes according to the invention remove contaminants from the slop fraction 165. That is, the process removes at least one contaminant. It is understood that the slop fraction 165 will usually comprise a plurality of contaminants of different types in various amounts. Thus, the process removes at least a portion of at least one type of contaminant. The process may remove the same or different amounts of each type of contaminant, and some types of contaminants may not be removed.

One or more ionic liquids can be used in the process.

The ionic liquid comprises an organic cation and an anion. Suitable organic cations include, but are not limited to:

where R¹-R²¹ are independently selected from C₁-C₂₀ hydrocarbons, C₁-C₂₀ hydrocarbon derivatives, halogens, and H. Suitable hydrocarbons and hydrocarbon derivatives include saturated and unsaturated hydrocarbons, halogen substituted and partially substituted hydrocarbons and mixtures thereof. C₁-C₈ hydrocarbons are particularly suitable.

The anion can be derived from halides, sulfates, bisulfates, nitrates, sulfonates, fluoroalkanesulfonates, and combinations thereof. The anion is typically derived from metal and nonmetal halides, such as metal and nonmetal chlorides, bromides, iodides, fluorides, or combinations thereof. Combinations of halides include, but are not limited to, mixtures of two or more metal or nonmetal halides (e.g., AlCl₄ ⁻ and BF₄ ⁻), and mixtures of two or more halides with a single metal or nonmetal (e.g., AlCl₃Br⁻). In some embodiments, the metal is aluminum, with the mole fraction of aluminum ranging from 0<Al<0.25 in the anion. Suitable anions include, but are not limited to, AlCl₄ ⁻, Al₂Cl₇ ⁻, Al₃Cl₁₀ ⁻, AlCl₃Br⁻, Al₂Cl₆Br⁻, Al₃Cl₉Br⁻, AlBr₄ ⁻, Al₂Br₇ ⁻, Al₃Br₁₀ ⁻, GaCl₄ ⁻, Ga₂Cl₇ ⁻, Ga₃Cl₁₀ ⁻, GaCl₃Br⁻, Ga₂Cl₆Br⁻, Ga₃Cl₉Br⁻, CuCl₂ ⁻, Cu₂Cl₃ ⁻, Cu₃Cl₄ ⁻, ZnCl₃ ⁻, FeCl₃ ⁻, FeCl₄ ⁻, Fe₃Cl₇ ⁻, PF₆ ⁻, and BF₄ ⁻.

Consistent with common terms of art, the ionic liquid introduced to the contaminant removal step may be referred to as a “lean ionic liquid” generally meaning a hydrocarbon-immiscible ionic liquid that is not saturated with one or more extracted contaminants. Lean ionic liquid may include one or both of fresh and regenerated ionic liquid and is suitable for accepting or extracting contaminants from the hydrocarbon feed. Likewise, the ionic liquid effluent may be referred to as “rich ionic liquid”, which generally means a hydrocarbon-immiscible ionic liquid effluent produced by a contaminant removal step or process or otherwise including a greater amount of extracted contaminants than the amount of extracted contaminants included in the lean ionic liquid. A rich ionic liquid may require regeneration or dilution, e.g. with fresh ionic liquid, before recycling to the same or another contaminant removal step of the process.

In an embodiment, the contaminant removal comprises a contacting step and a separating step. In the contacting step, the slop fraction 165 comprising a contaminant and a hydrocarbon-immiscible ionic liquid are contacted or mixed. The contacting may facilitate transfer or extraction of the one or more contaminants from the slop fraction 165 to the ionic liquid. Although an ionic liquid that is partially soluble in the hydrocarbon may facilitate transfer of the contaminant from the hydrocarbon to the ionic liquid, partial solubility is not required. Insoluble hydrocarbon/ionic liquid mixtures may have sufficient interfacial surface area between the hydrocarbon and ionic liquid to be useful. In the separation step, the mixture of hydrocarbon and ionic liquid settles or forms two phases, a hydrocarbon phase and an ionic liquid phase, which are separated to produce a hydrocarbon-immiscible ionic liquid effluent and a hydrocarbon effluent.

The decontamination process may be conducted in various equipment which is well known in the art and is suitable for batch or continuous operation. For example, in a small scale form of the invention, hydrocarbon and a hydrocarbon-immiscible ionic liquid may be mixed in a beaker, flask, or other vessel, e.g., by stirring, shaking, use of a mixer, or a magnetic stirrer. The mixing or agitation is stopped and the mixture forms a hydrocarbon phase and an ionic liquid phase which can be separated, for example, by decanting, centrifugation, or use of a pipette to produce a hydrocarbon effluent having a lower contaminant content relative to the incoming hydrocarbon. The process also produces a hydrocarbon-immiscible ionic liquid effluent comprising the one or more contaminants.

The contacting and separating steps may be repeated, for example, when the contaminant content of the hydrocarbon effluent is to be reduced further to obtain a desired contaminant level in the ultimate hydrocarbon product stream from the process. Each set, group, or pair of contacting and separating steps may be referred to as a contaminant removal step. Thus, the invention encompasses single and multiple contaminant removal steps. A contaminant removal zone may be used to perform a contaminant removal step. As used herein, the term “zone” can refer to one or more equipment items and/or one or more sub-zones. Equipment items may include, for example, one or more vessels, heaters, separators, exchangers, conduits, pumps, compressors, and controllers. Additionally, an equipment item can further include one or more zones or sub-zones. The contaminant removal process or step may be conducted in a similar manner and with similar equipment as is used to conduct other liquid-liquid wash and extraction operations. Suitable equipment includes, for example, columns with: trays, packing, rotating discs or plates, and static mixers. Pulse columns and mixing/settling tanks may also be used.

The slop fraction 165 is contacted with the lean ionic liquid 180 in the contaminant removal zone 175. The contaminants are transferred from the slop fraction 165 to the lean ionic liquid 180. The treated slop effluent 185 has considerably less contaminants than the untreated slop fraction 165.

The lean ionic liquid stream 180 may be comprised of fresh ionic liquid stream and/or one or more ionic liquid streams which are recycled in the process as described below.

The contact step can take place at a temperature in the range of about 20° C. to the decomposition temperature of the ionic liquid, or about 20° C. to about 120° C., or about 20° C. to about 80° C.

The contacting time is sufficient to obtain good contact between the ionic liquid and the hydrocarbon feed. The contacting time is typically in the range of about 1 min to about 1 hr, or about 5 min to about 30 min.

An optional washing step (not shown) may be used, for example, to recover ionic liquid that is entrained or otherwise remains in the treated slop effluent 185 by using water to wash or extract the ionic liquid from the hydrocarbon effluent. In this embodiment, a portion or all of treated slop effluent 185 (as feed) and a water stream (as solvent) are introduced to a washing zone. The treated slop effluent 185 and water streams are mixed and separated to produce a washed treated slop effluent 185 and a spent water stream, which comprises the ionic liquid. The washing step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed above. Various hydrocarbon washing step equipment and conditions such as temperature, pressure, times, and solvent to feed ratio may be the same as or different from the contaminant removal zone equipment and conditions. In general, the hydrocarbon washing step conditions will fall within the same ranges as given below for the contaminant removal step conditions.

An optional ionic liquid regeneration step may be used, for example, to regenerate the ionic liquid by removing the contaminant from the ionic liquid, i.e. reducing the contaminant content of the rich ionic liquid. In an embodiment, a portion or all of rich ionic liquid stream 190 (as feed) comprising the contaminant and a regeneration solvent stream 195 are introduced to ionic liquid regeneration zone 200. The rich ionic liquid stream 190 and regeneration solvent stream 195 are mixed and separated to produce an extract stream 205 comprising the contaminant, and a regenerated ionic liquid stream 210. The ionic liquid regeneration step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed below. Various ionic liquid regeneration step conditions such as temperature, pressure, times, and solvent to feed may be the same as or different from the contaminant removal conditions. In general, the ionic liquid regeneration step conditions will fall within the same ranges as given below for the contaminant removal step conditions.

In an embodiment, the regeneration solvent stream 195 comprises a hydrocarbon fraction lighter than the slop fraction 165 and which is immiscible with the ionic liquid. The lighter hydrocarbon fraction may consist of a single hydrocarbon compound or may comprise a mixture of hydrocarbons. In an embodiment, the lighter hydrocarbon fraction may comprise at least one of a naphtha, gasoline, diesel, light cycle oil (LCO), and light coker gas oil (LCGO) hydrocarbon fraction. The lighter hydrocarbon fraction may comprise straight run fractions and/or products from conversion processes such as hydrocracking, hydrotreating, fluid catalytic cracking (FCC), reforming, coking, and visbreaking. In this embodiment, extract stream 205 comprises the lighter hydrocarbon regeneration solvent and the contaminant. In another embodiment, the regeneration solvent stream 195 comprises water, and the ionic liquid regeneration step produces an extract stream 205 comprising the contaminant and the regenerated ionic liquid 210 comprising water and the ionic liquid. In an embodiment wherein regeneration solvent stream 195 comprises water, a portion or all of spent water stream from the water washing step may provide a portion or all of regeneration solvent stream 195. Regardless of whether regeneration solvent stream 195 comprises a lighter hydrocarbon fraction or water, a portion or all of regenerated ionic liquid stream 210 may be recycled to the contaminant removal step. For example, a constraint on the water content of the lean ionic liquid stream 180 or the ionic liquid/hydrocarbon mixture in contaminant removal zone 175 may be met by controlling the proportion and water content of fresh and recycled ionic liquid streams.

The extract stream 205 containing the contaminants removed from the rich ionic liquid stream 190 can be combined with the vacuum residue fraction 170 from the vacuum tower 145 and sent for further processing or kept separate from the vacuum residue fraction.

The treated slop effluent 185 can be combined with the LVGO fraction 155, the HVGO fraction 160, or a combined LVGO/HVGO stream 155/160 and sent to the downstream processing unit 208, such as the hydrocracking unit or an FCC unit.

The process can include an optional ionic liquid drying step (not shown). The ionic liquid drying step may be employed to reduce the water content of one or more of the streams comprising ionic liquid to control the water content of the contaminant removal step as described above. A portion or all of regenerated ionic liquid stream 210 can be introduced to a drying zone. Other streams comprising ionic liquid may also be dried in the drying zone. To dry the ionic liquid stream or streams, water may be removed by one or more various well known methods including distillation, flash distillation, and using a dry inert gas to strip water. Generally, the drying temperature may range from about 100° C. to less than the decomposition temperature of the ionic liquid, usually less than about 300° C. The pressure may range from about 35 kPa(g) to about 250 kPa(g). The drying step produces a dried ionic liquid stream and a drying zone water effluent stream. Although not illustrated, a portion or all of the dried ionic liquid stream may be recycled or passed to provide all or a portion of the ionic liquid introduced to the contaminant removal zone 175. A portion or all of drying zone water effluent stream may be recycled or passed to provide all or a portion of the water introduced into the optional washing zone and/or ionic liquid regeneration zone 200.

FIG. 2A illustrates an embodiment the contaminant removal zone 175. It comprises a multi-stage, counter-current extraction column 210 in which the slop fraction 165 and the lean ionic liquid 180 are contacted and separated. The slop fraction 165 enters extraction column 210 through feed inlet 215 and lean ionic liquid stream 180 enters extraction column 210 through ionic liquid inlet 220. In the FIGURES, reference numerals of the streams and the lines or conduits in which they flow are the same. The slop fraction inlet 215 is located below ionic liquid inlet 220. The treated slop effluent 185 passes through outlet 225 in an upper portion of extraction column 210. The rich ionic liquid 190 including the contaminants removed from the hydrocarbon feed passes through ionic liquid outlet 230 in a lower portion of extraction column 210.

FIG. 2B illustrates another embodiment of contaminant removal zone 175 that comprises a contacting zone 235 and a separation zone 240. In this embodiment, lean ionic liquid stream 180 and slop fraction 165 are introduced into the contacting zone 235 and mixed by introducing slop fraction 165 into the flowing lean ionic liquid stream 180 and passing the combined streams through static in-line mixer 245. Static in-line mixers are well known in the art and may include a conduit with fixed internals such as baffles, fins, and channels that mix the fluid as it flows through the conduit. In other embodiments, not illustrated, lean ionic liquid stream 180 may be introduced into slop fraction 165, or the lean ionic liquid stream 180 and slop fraction 165 may be combined such as through a “Y” conduit. In another embodiment, lean ionic liquid stream 180 and slop fraction 165 are separately introduced into the static in-line mixer 245. In other embodiments, the streams may be mixed by any method well known in the art, including stirred tank and blending operations. The mixture comprising hydrocarbon and ionic liquid is transferred to separation zone 240 via transfer conduit 250. Separation zone 240 comprises separation vessel 225 wherein the two phases are allowed to separate into a rich ionic liquid phase and a hydrocarbon phase. The rich ionic liquid stream 190 is withdrawn from a lower portion of separation vessel 225 and the treated slop effluent 185 is withdrawn from an upper portion of separation vessel 225. Separation vessel 225 may comprise a boot, not illustrated, from which rich ionic liquid is withdrawn.

Separation vessel 225 may contain a solid media 260 and/or other coalescing devices which facilitate the phase separation. In other embodiments, the separation zone 240 may comprise multiple vessels which may be arranged in series, parallel, or a combination thereof. The separation vessels may be of any shape and configuration to facilitate the separation, collection, and removal of the two phases. In a further embodiment, contaminant removal zone 175 may include a single vessel wherein lean ionic liquid stream 180 and slop fraction 165 are mixed, then remain in the vessel to settle into the hydrocarbon and rich ionic liquid phases.

In an embodiment, the process comprises at least two contaminant removal steps. For example, the hydrocarbon effluent from one contaminant removal step may be passed directly as the hydrocarbon feed to a second contaminant removal step. In another embodiment, the hydrocarbon effluent from one contaminant removal step may be treated or processed before being introduced as the hydrocarbon feed to the second contaminant removal step. There is no requirement that each contaminant removal zone comprises the same type of equipment. Different equipment and conditions may be used in different contaminant removal zones.

The contaminant removal step may be conducted under contaminant removal conditions including temperatures and pressures sufficient to keep the hydrocarbon-immiscible ionic liquid and hydrocarbon feeds and effluents as liquids. For example, the contaminant removal step temperature may range between about 10° C. and less than the decomposition temperature of the ionic liquid, and the pressure may range between about atmospheric pressure and about 700 kPa(g). When the hydrocarbon-immiscible ionic liquid comprises more than one ionic liquid component, the decomposition temperature of the ionic liquid is the lowest temperature at which any of the ionic liquid components decompose. The contaminant removal step may be conducted at a uniform temperature and pressure or the contacting and separating steps of the contaminant removal step may be operated at different temperatures and/or pressures. In an embodiment, the contacting step is conducted at a first temperature, and the separating step is conducted at a temperature at least 5° C. lower than the first temperature. In a non limiting example, the first temperature is about 80° C. Such temperature differences may facilitate separation of the hydrocarbon and ionic liquid phases.

The above and other contaminant removal step conditions such as the contacting or mixing time, the separation or settling time, and the ratio of hydrocarbon feed to hydrocarbon-immiscible ionic liquid (lean ionic liquid) may vary greatly based, for example, on the specific ionic liquid or liquids employed, the nature of the hydrocarbon feed (straight run or previously processed), the contaminant content of the hydrocarbon feed, the degree of contaminant removal required, the number of contaminant removal steps employed, and the specific equipment used. In general, it is expected that contacting time may range from less than one minute to about two hours; settling time may range from about one minute to about eight hours. The weight ratio of hydrocarbon feed to lean ionic liquid introduced to the contaminant removal step may range from about 1:10,000 to about 10,000:1, or about 1:1,000 to about 1,000:1, or about 1:100 to about 100:1, or about 1:20 to about 20:1, or about 1:10 to about 10:1. In an embodiment, the weight of hydrocarbon feed is greater than the weight of ionic liquid introduced to the contaminant removal step.

In an embodiment, a single contaminant removal step reduces the contaminant content of the hydrocarbon by more than about 10 wt %, or more than about 20 wt %, or more than about 30 wt %, or more than about 40 wt %, or more than about 50 wt %, or more than about 60 wt %, or more than about 70 wt %, or more than about 75 wt %, or more than about 80 wt %, or more than about 85 wt %, or more than about 90 wt %. As discussed herein, the invention encompasses multiple contaminant removal steps to provide the desired amount of contaminant removal.

The degree of phase separation between the hydrocarbon and ionic liquid phases is another factor to consider as it affects recovery of the ionic liquid and hydrocarbon. The degree of contaminant removed and the recovery of the hydrocarbon and ionic liquid may be affected differently by the nature of the hydrocarbon feed, the variations in the specific ionic liquid or liquids, the equipment, and the contaminant removal conditions such as those discussed above.

The amount of water present in the hydrocarbon/hydrocarbon-immiscible ionic liquid mixture during the contaminant removal step may also affect the amount of contaminant removed and/or the degree of phase separation, i.e., recovery of the hydrocarbon and ionic liquid. In an embodiment, the hydrocarbon/hydrocarbon-immiscible ionic liquid mixture has a water content of less than about 10% relative to the weight of the ionic liquid, or less than about 5% relative to the weight of the ionic liquid, or less than about 2% relative to the weight of the ionic liquid. In a further embodiment, the hydrocarbon/hydrocarbon-immiscible ionic liquid mixture is water free, i.e., the mixture does not contain water.

Unless otherwise stated, the exact connection point of various inlet and effluent streams within the zones is not essential to the invention. For example, it is well known in the art that a stream to a distillation zone may be sent directly to the column, or the stream may first be sent to other equipment within the zone such as heat exchangers, to adjust temperature, and/or pumps to adjust the pressure. Likewise, streams entering and leaving contaminant removal, washing, and regeneration zones may pass through ancillary equipment such as heat exchanges within the zones. Streams, including recycle streams, introduced to washing or extraction zones may be introduced individually or combined prior to or within such zones.

The invention encompasses a variety of flow scheme embodiments including optional destinations of streams, splitting streams to send the same composition, i.e. aliquot portions, to more than one destination, and recycling various streams within the process. Examples include: various streams comprising ionic liquid and water may be dried and/or passed to other zones to provide all or a portion of the water and/or ionic liquid required by the destination zone. The various process steps may be operated continuously and/or intermittently as needed for a given embodiment e.g. based on the quantities and properties of the streams to be processed in such steps. As discussed above the invention encompasses multiple contaminant removal steps, which may be performed in parallel, sequentially, or a combination thereof. Multiple contaminant removal steps may be performed within the same contaminant removal zone and/or multiple contaminant removal zones may be employed with or without intervening washing, regeneration and/or drying zones.

By the term “about,” we mean within 10% of the value, or within 5%, or within 1%.

EXAMPLES

The examples are presented to further illustrate some aspects and benefits of the invention and are not to be considered as limiting the scope of the invention.

A simulation was run for Arab Heavy crude being processed though a crude and vacuum distillation unit as illustrated in FIG. 1 with conventional product being drawn from it. The simulation showed that by choosing the slop fraction and VGO endpoint appropriately, the contaminants in the VGO fraction can be limited to acceptable levels. The slop fraction, which has more contaminants, can be treated with the ionic liquid. The treated slop fraction can then be blended with the VGO stream to maximize the throughput to the hydroprocessing and/or FCC unit, thus maximizing the desired products.

Table 1 gives the true boiling point (TBP) and some properties for Arab Heavy crude.

TABLE 1 TBPCRV C IBP −8.65741  5% 42.40527 10% 96.69801 30% 228.18 50% 362.0511 70% 504.1968 90% 695.1002 100%  854.1088 spgr 0.874 S wpct 2.715 N wppm 1407 Ni wppm 1234 Va wppm 3970 CCR wppm 68624

The initial boiling point for VGO is 315° C. (TBP), and the final boiling point for VGO is 520° C. (TBP). The initial boiling point for the slop fraction is 388° C. (true boiling point (TBP)), and the final boiling point for the slop fraction is 570° C. (TBP). This data is for one set of operating conditions. The final boiling points can be changed based on how the refiner wants to charge the downstream unit, e.g., the hydrocracking unit.

Example 1

Tetrabutyl phosphonium methansulfonate, which is mainly selective for removal of metals and nitrogen, was used for this simulation. Table 2 shows the results for this simulation.

TABLE 2 Removal (%) across Treated Blend ionic Slops (ex (VGO + liquid Ionic liq Treated VGO SLOPS treatment treatment) Slops) Flow lb/hr 140370 6614 6614 146984 S wpct 2.94 3.504 5.2 3.322 2.957 N wppm 581.4 1024 71.4 292.864 568.416 Ni wppm 0.59 24.09 86 3.373 0.715 Va wppm 1.83 76.2 68.4 24.079 2.831

Example 2

In this example, a mixture of tetrabutyl phosphonium methansulfonate, trihexyl(tetradecyl)phosphonium chloride, and 1-butyl-3-methylimidazolium trifluoromethansulfonate was used for the simulation. Table 3 shows the results of this simulation.

TABLE 3 Removal (%) across Treated Blend ionic Slops (ex (VGO + liquid Ionic liq Treated VGO SLOPS treatment treatment) Slops) Flow lb/hr 140370 6614 6614 146984 S wpct 2.94 3.504 64.5 1.244 2.864 N wppm 581.4 1024 84.7 156.672 562.288 Ni wppm 0.59 24.09 86 3.373 0.715 Va wppm 1.83 76.2 68.4 24.079 2.831

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. A process for increasing vacuum gas oil recovery from a vacuum column comprising: separating a residue crude oil stream from a crude oil separation column in a vacuum column into at least one vacuum gas oil fraction, and a contaminant-rich slop fraction containing at least one contaminant; contacting the contaminant-rich slop fraction with a lean ionic liquid in a contaminant removal zone to produce a mixture comprising a contaminant-lean slop fraction and a rich ionic liquid comprising at least a portion of the at least one contaminant; and separating the mixture to produce a treated slop effluent comprising the contaminant-lean slop fraction and a rich ionic liquid effluent comprising the rich ionic liquid.
 2. The process of claim 1 further comprising introducing the treated slop effluent into a secondary conversion zone comprising at least one of a hydrocracking or a hydrotreating zone and a fluid catalytic cracking zone.
 3. The process of claim 2 further comprising: combining the treated slop effluent with the at least one vacuum gas oil fraction to form a combined fraction before introducing the treated slop effluent into the secondary conversion zone.
 4. The process of claim 1 further comprising regenerating the rich ionic liquid effluent to remove at least a portion of the at least one contaminant from the rich ionic liquid effluent forming a regenerated ionic liquid and an extract stream containing at least the portion of the at least one contaminant.
 5. The process of claim 4 further comprising separating the regenerated ionic liquid from the extract stream.
 6. The process of claim 5 further comprising recycling the regenerated ionic liquid to the treatment zone.
 7. The process of claim 5 wherein separating the residue crude oil stream from the crude oil separation column in the vacuum column into the at least one vacuum gas oil fraction, and the contaminant-rich slop fraction comprises separating the residue crude oil stream from the crude oil separation column in the vacuum column into the at least one vacuum gas oil fraction, the contaminant-rich slop fraction, and a vacuum residue fraction; and further comprising combining the extract stream with the vacuum residue fraction.
 8. The process of claim 7 further comprising introducing the combined extract stream and vacuum residue fraction to a delayed coker zone.
 9. The process of claim 1 wherein the contaminant-rich slop fraction comprises between about 5 wt % to about 30 wt % of a total of the at least one vacuum gas oil fractions.
 10. The process of claim 1 wherein the at least one vacuum gas oil fraction comprises a light vacuum gas oil fraction and a heavy vacuum gas oil fraction.
 11. The process of claim 1 wherein the contaminant-rich slop fraction has a boiling point in a range of about 490° C. to about 565° C.
 12. The process of claim 1 wherein the ionic liquid comprises an organic cation and an anion, and wherein the organic cation is selected from the group consisting of:

where R¹-R²¹ are independently selected from C₁-C₂₀ hydrocarbons, C₁-C₂₀ hydrocarbon derivatives, halogens, and H.
 13. The process of claim 1, wherein the ionic liquid comprises an organic cation and an anion, and wherein the anion comprises at least one of a carboxylate, an acetate, a tosylate, a cyanate, a halide, a sulfate, a hydrogen sulfate, a sulfonate, a sulfonyl imide, a phosphate, a borate, a carbonate, or a heterocyclic anion.
 14. A process for increasing the vacuum gas oil recovery from a vacuum column comprising: separating a residue crude oil stream from a crude oil separation column in a vacuum column into at least one vacuum gas oil fraction, a contaminant-rich slop fraction containing at least one contaminant, and a vacuum residue fraction; contacting the contaminant-rich slop fraction with a lean ionic liquid in a contaminant removal zone to produce a mixture comprising a contaminant-lean slop fraction and a rich ionic liquid comprising at least a portion of the at least one contaminant; separating the mixture to produce a treated slop effluent comprising the contaminant-lean slop fraction and a rich ionic liquid effluent comprising the rich ionic liquid; introducing the treated slop effluent into a secondary conversion zone comprising at least one of a hydrocracking zone, a fluid catalytic cracking zone, and a VGO hydrotreating zone; and regenerating the rich ionic liquid effluent to remove at least a portion of the at least one contaminant from the rich ionic liquid effluent forming a regenerated ionic liquid and an extract stream containing at least the portion of the at least one contaminant.
 15. The process of claim 14 further comprising: combining the treated slop effluent with the at least one vacuum gas oil fraction to form a combined fraction before introducing the treated slop effluent into the secondary conversion zone.
 16. The process of claim 14 further comprising separating the regenerated ionic liquid from the extract stream.
 17. The process of claim 14 further comprising recycling the regenerated ionic liquid to the treatment zone.
 18. The process of claim 14 wherein the contaminant-rich slop fraction comprises between about 5 wt % to about 30 wt % of a total of the at least one vacuum gas oil fractions.
 19. The process of claim 14 wherein the contaminant-rich slop fraction has a boiling point in a range of about 490° C. to about 565° C.
 20. An apparatus for increasing vacuum gas oil recovery comprising: a crude oil separation column having an inlet and at least a bottom outlet; a vacuum column having an inlet and at least an upper and a lower outlet, the inlet of the vacuum column being in fluid communication with the bottom outlet of the crude oil separation column; a contaminant removal zone having an inlet and an outlet, the inlet of the contaminant removal zone being in fluid communication with the lower outlet of the vacuum column; a secondary conversion zone having an inlet and an outlet, the inlet of the secondary conversion zone being in fluid communication with the upper outlet of the vacuum column and the outlet of the contaminant removal zone. 